The present invention relates to a method for rapid mixing of ethane and chlorine gases. More particularly, it relates to a method of mixing hot ethane with chlorine, which gases undergo immediate exothermic chemical reaction upon contact. Several U.S. patents disclose reactions of ethane and chlorine and processes in which the gases must be mixture, for example, U.S. Pat. Nos. 2,259,195; 2,628,259; 2,838,579; and 3,166,601. U.S. Pat. Nos. 2,259,195 and 2,628,259 also disclose the mixing of chlorine with hot ethane. Hot ethane and chlorine react rapidly and exothermically and will form side products such as carbon unless mixing is accomplished quickly. Applicants' invention is useful in that it provides a process for the rapid mixing of hot ethane and chlorine.
The Kirk-Othmer Encyclopedia of Chemical Technology (2nd edition, volume 13, p. 577) indicates that there are several methods of mixing gases. However, they all seem to work by inducing turbulence which causes the gases to mix. Basically, turbulence is induced by causing high velocity streams to collide with each other, or by allowing one stream of gas to expand, through an orifice, into another stream of gas. A mixing tee is a well-known technique for mixing gases. In this technique, a gas flows through a straight pipe, and a second gas is injected at a right angle to the direction of travel of the first gas.
Chilton and Genereaux, Trans. Am. Inst. Chem. End. Grs., 25, 103 (1930), describes their results with such a mixing tee. Although they obtain good results, with non-reactive gases, we were not able to duplicate their results with reactive gases. In Comparative Example 1, results of attempts to mix chlorine with hot ethane are shown. In this system, the reaction begins quickly and is so exothermic that if the mixing is not complete, localized hot spots will result in the formation of carbon. The simple mixing tee did not provide adequate mixing, but instead resulted in a great deal of carbon formation.
L. J. Forney, (Jet Injection for Optimum Pipeline Mixing, Encyclopedia of Fluid Mechanics; Cheremisinoff, ed., vol II, Ch. 25, pp. 660-690, Gulf Publishing Company, Houston, 1986), has studied single and dual-jet mixers. One mixer which he studied in detail has two jets on opposite sides of the pipe through which the main stream of gas is flowing. The jets are not directed toward the center of the circle, but rather the angle between the axis of the jet and the radius drawn to the point of entry is 45.degree.. While Forney provides equations to describe mixing, he states that in using the equations, problems can arise when attempting to use the equations to achieve optimum mixing, "particularly when the ratio of jet to pipe diameter is small and the measurement point is less than ten pipe diameters from the injection point." When the gases to be mixed react rapidly, and exothermically, mixing must be accomplished in much quicker than ten pipe diameters if it is to be effective.
As set forth in Comparative Example 1, when hot ethane was mixed with chlorine, carbon deposition due to poor mixing began within two pipe diameters of the mixing point. In other words, if the mixing is not complete within two pipe diameters, problems from side reactions due to poor mixing will occur. Accordingly, the equations of Forney, which are useful at distances of ten pipe diameters from the injection point, are of little help in solving the mixing problem that Applicants face.
Maruyama, Mizushina, and Hayashiguchi, International Chemical Engineering, vol. 23, 707 (1983), studied the optimal conditions for jet mixing in turbulent pipe flow. The apparatus used was described in a prior reference, Toshiro Maruyama, Kagaku Kogaku Ronbunshu, vol. 7, no. 3, pp 215-221 (1981). The authors studied both single and dual jet injectors at various angles of injection. In this study, the main pipe has a circular cross-section and the inlet jets are directed at various angles. The angle of injection is defined as the angle between the axis of the inlet jet and the line connecting the point o intersection of the inlet jet access in the inner wall of the main pipe with the center of the main pipe. The authors studied dual jet mixers at 0.degree., that is, two jets directed directly at each other pointing at the center of the pipe, two jets at angles of .pi./6 radians (30.degree.), two jets at injection angles of .pi./4 radians (45.degree.), and two jets tangential to the inner walls of the main pipe. They observed that the optimal angle for injection was 30.degree.. However, on page 715, their graphs also indicate that whatever conditions they chose, complete mixing was not obtained in less than five diameters of the main pipe. They also noted that in the case of tangential injection, where the two injection jets could interact, the mixing of the inlet jets with each other suppressed their mixing with the main stream. If tangential mixing is to be employed, the authors state that the velocity ratio of the inlet gas stream to the main gas stream should be lower to prevent the interaction of the two inlet gas streams.
Studies in our laboratory have shown that other methods of mixing gas streams likewise did not serve to mix hot ethane and chlorine. Specifically, we tested coaxial, venturi, fritted disk, and fluidized bed mixers. As set forth in the comparative examples, in each case, carbon formation was a problem. Carbon appears in several forms, including sooty, soft deposits and hard, coal-like deposits. Of course, all carbon formation is undesirable because it represents a loss of starting material. In addition, the fine carbon is a nuisance in handling the gases after mixing. Both the soft deposits and the hard deposits can actually block gas flow in the mixer. The hard carbon deposits are particularly difficult to remove from the mixer.